Conventional medium and heavy duty trucks have a large engine covering hood which tilts about a transverse pivot axis located above the bumper to expose the engine for servicing. Although commonly made of lightweight materials, these hoods are nevertheless heavy and cumbersome in part because of the relatively long moment arm between the center of gravity of the hood and the pivot axis. In addition to the mass of the hood, there is also the problem of arresting its movement toward either the open or closed position.
Various devices for dealing with these problems have been used including counterbalance springs, cables, shock absorbers, and gas springs. In particular, U.S. Pat. No. 3,419,099 to Brumbaugh et al teaches an air assist cylinder connected between the vehicle frame and the hood. Disposed within the cylinder between the piston and the rod end is a compression spring which acts to cushion the movement of the hood toward the open position.